Power jaw-type grippers are known to be of the type in which a fluid motor provides reciprocating movement to a mechanical linkage for actuating the jaw type grippers. Normally, the fluid motor retracts the reciprocating actuator, and through a mechanical linkage, the jaws of the gripper pivot away from one another thus releasing and disengaging the workpiece. When the fluid motor actuates the reciprocating actuator toward a clamped position, the mechanical linkage drives the jaws of the gripper toward one another to engage and hold the workpiece.
Various mechanical linkages have been proposed to correctly translate reciprocating movement of a piston and piston rod to optimize the clamping force of the gripper jaws by seeking to obtain the highest mechanical advantage which can be utilized by the power stroke of the fluid motor and the mechanical linkage of the power gripper. All of these known mechanisms, more or less, include complex designs of various mechanical components at high manufacturing and assembly cost.
Occasionally, the clamping forces generated by the mechanical linkage of the power gripper are not sufficient as the work performed on the workpiece may generate or apply forces to the workpiece which are greater than the gripping forces applied by the gripper. In addition, the clamping forces generated by the mechanical linkage of the power gripper may not be sufficient to sustain the weight of the workpiece or the momentum created upon movement of the workpiece. Different geometrical configurations of the workpiece may make it difficult for the jaws of the power gripper to grasp and retain the workpiece upon engaging and moving the workpiece.
When power actuated grippers are utilized in a production environment, the power actuated grippers may lose fluid power to the fluid motor, i.e. the supply of pressurized air or hydraulic fluid may be cut-off to the fluid motor. If the grippers have engaged a workpiece in the clamped position when power is cut-off to the fluid motor, it is desirable not to have the jaws of the power gripper release the workpiece. Several known designs have been utilized to lock the grippers in the clamped position and prevent unpowered movement of the grippers from the clamped position, but such designs typically utilize rollers or over center linkage mechanisms which require high actuation forces as well as accelerated wear rates with respect to the linkage mechanisms.
Therefore, it would be desirable to provide a power actuated gripper that provides high gripping forces while also prohibiting unpowered movement of the grippers from a clamped position.